1. Field of the Invention
The present invention relates to a developing cartridge that is freely mountable in and removable from an image forming device.
2. Description of Related Art
Color laser printers are capable of forming images in full color. A color laser printer is provided with a plurality of different developing cartridges, each holding a different color of toner. The developing cartridges are freely mountable in and removable from the laser printer.
Each developing cartridge includes a housing, a developing roller, a layer thickness regulating blade, and a supply roller. The housing is formed with a toner holding chamber that holds the toner in the color that corresponds to the developing cartridge. The developing roller, the layer thickness regulating blade, and the supply roller are housed in the housing. The toner contained in the toner holding chamber is supplied to the developing roller by the supply roller. The toner supplied to the developing roller passes between the developing roller and the layer thickness regulating blade and is regulated to a thin layer of uniform thickness on the surface of the developing roller.
The color laser printer further includes a photosensitive member and an exposure unit. The photosensitive member is formed with a photosensitive layer at its outer surface. The exposure unit selectively exposes the photosensitive layer to laser light to form an electrostatic latent image on the photosensitive member. When the developing cartridges are mounted in the casing of the color laser printer, the developing roller of each developing cartridge is disposed in confrontation with photosensitive member so that the toner borne on the surface of the developing roller develops the electrostatic latent image into a visible toner image.
The visible toner images in each different color of toner are transferred on top of each other onto a sheet to form a color image on the sheet.
Leaf-spring type electrodes are provided on the casing of the laser printer at positions that correspond to the developing cartridges. Each leaf-spring type electrode is connected to a high-voltage source that is housed within the casing and applies developing bias to the developing roller of the corresponding developing cartridge. That is, each leaf-spring type electrode abuts against the end of the roller shaft of the corresponding developing roller, that is, while the developing cartridge is fully mounted in the casing of the laser printer.
When one of the developing cartridges is mounted into the casing of the laser printer, the end of the roller shaft moves into confrontation with and presses against the corresponding leaf-spring type electrode. This brings the roller shaft into electrical connection with the high-voltage source so that the developing bias from the high-voltage source can be applied to the developing roller. At this time, the leaf-spring type electrode resiliently bends under the pressing force of the roller shaft. The resultant urging force form the leaf-spring type electrode maintains good contact between the leaf-spring type electrode and the roller shaft.